The present invention relates to improvements in a usually cylindrical mandrel for manufacturing golf club shafts, and to an improved golf club shaft manufactured therewith.
A conventional type known golf club shaft comprising reinforced fiber is constructed such that a sheet of reinforced fiber impregnated with a thermosetting resin, or a bundle of reinforced fiber also impregnated with a thermosetting resin is wrapped around or wound on to the outer circumferential surface of a mandrel gradually decreased in the diameter thereof in a tapered or multistage configuration from the basic end portion thereof to the terminal end portion thereof, and after the resin has set or hardened around the outer circumferential surface of the mandrel, the mandrel is extracted from the layer of the reinforced fiber surrounding it, in the direction of the basic end portion thereof which has a larger diameter.
The conventional golf club shaft constructed in the foregoing manufacturing method is gradually increased in the rigidity thereof from the terminal end portion of a smaller diameter thereof to the basic end portion of a larger diameter thereof, because the mandrel for manufacturing the golf club shaft is gradually reduced in the diameter thereof from the basic end portion thereof to the terminal end portion thereof. However, this construnction of the golf club shaft does not allow the rigidity thereof to be locally enlarged, and in fact, it reduces or limits the designing freedom to set what is called the low bending point and the high bending point freely in any desired place of the golf club shaft, and another designing freedom to distribute the weight, strength and the like of the golf club shaft therein as desired. This is a disadvantage of the conventional golf club shaft or the conventional mandrel for manufacturing it.
It is therefore an object of the present invention to provide an improved golf club shaft in which the foregoing disadvantage of the conventional golf club shaft is overcome, and the designing freedom is enhanced, thereby allowing the golf club shaft to be locally adjusted in the weight or strength distribution, and rigidity thereof.
It is also an object of the present invention to provide an improved mandrel for forming the foregoing improved golf club shaft of the present invention, in which the foregoing disadvantage of the conventional mandrel for manufacturing the conventional golf club shaft is overcome.